1. Scope of Invention
This invention relates generally to metal plating and more particularly to improved uniform plated microspheres for use in catalytic processes and electrical applications.
2. Prior Art
In U.S. Pat. No. 3,577,324, I described a process and apparatus for plating particles which had as a preferred embodiment the plating of polymeric beads formed from polystyrene cross-linked with divinyl benzene. A solution for bonding copper atoms to such beads was disclosed.
In U.S. Pat. No. 3,787,718, I disclosed the use of plated spherical particles as electronic components. In this patent, the forming of additional coatings or platings on the copper layer was also disclosed.
U.S. Pat. No. 2,915,406 to Rhoda et al., entitled "Palladium Plating by Chemical Reduction", discloses a number of baths for use in immersion plating of various metals.
Another of my earlier patents, U.S. Pat. No. 5,036,031, teaches a metal plated microsphere catalyst, the disclosure of which is incorporated herein by reference. This prior patent teaches the application of a copper plate of uniform thickness atop which a palladium plate is applied, the copper plate being applied atop microspheres formed of cross-linked polystyrene similar to my '324 patent.
In utilizing the microsphere catalyst disclosed in my '031 patent in the cell disclosed in my prior U.S. Pat. No. 5,372,688, I have observed a black residue forming within the liquid electrolyte of this cell. I have also observed shorter than expected cell life. Upon further investigation, I have determined that the source of the black residue is palladium which has been separated from the microsphere catalyst beads under heat and electrical current duty cycle.
The present invention discloses the preparation of copolymer microspheres having copper salts on the outer portion. These microspheres are separated into batches of substantially uniform sizes and are then plated. By plating microspheres of the same size and density (as determined by Stoke's Law), a plating of uniform thickness can be achieved. This uniformly thick plating is essential when the plated microspheres are used in catalytic beds and/or with electric current flowing. Non-uniformly thick platings will result in hot spots which will cause the plating to spall off. An improved plated layer combination including a layer of nickel atop palladium is also disclosed which serves to structurally stabilize the palladium plate without inhibiting diffusion of hydrogen to palladium.